Protective device



Nov. 13, 1951 T. c. RIEBE PROTECTIVE DEVICE Filed April 5, 1950 TO LINEIN V EN TOR.

THEODORE C. RIEBE %Z 4 ATTORNEY Patented Nov. 13, 1951 2,574,888rnoracnva nmca Theodore C. Biebe, Automatic Electric Laboratories, Inc.,

111., a corporation of Delaware Application April 5, 1950, Serial No.154,093 8 Claims. (Cl. 200-115) This invention relates in general toprotective devices and more particularly to the thermal type ofprotective device for arresting abnormal voltages, lightning and thelike, likely to prove dangerous to life or destructive to property.

Accordingly, it is an object of the present invention to provide animproved thermal abnormal voltage protector which is reliable and testinoperation and which is operative to complete a direct ground circuit01 fixed low resistance.

Another object of the invention is to provide an improved thermalabnormal voltage protector which is simple in construction and compactin $128.

A further object oi the invention is to provide in an abnormal voltageprotector including in combination, serrated discharge members, animproved thermal member, a ground element and. a ceramic insulator formaintaining the aforementioned members in a given spaced relationship.

These and other objects and features will be more particularly pointedout and described in the ensuing specification and appended claims takenin conjunction with the accompanying drawings in which:

Fig. 1 is an exploded view of the protective de- V109.

Fig. 2 is a plan view of the protective device.

Fig. 3 is a cross sectional view of the device taken along line 33 inFig. 2.

In the preferred form as shown in the accompanying drawings, theabnormal voltage arrestor construction contemplates the use incombination of a carbon block type ground element I, serrated metallicdischarge members 2, a thermal bimetal member 3, refractory insulatingmember 4 and contact member 5. The serrated member 2 and bimetal member3 are positioned in spaced relationship with ground element I by meansof a refractory insulating member 4, and held in place by means ofprojections on a contact member 5, which projections are in registrywith apertures in said other members for receiving them.

In general, the contact member 5 is in electrical contact with a line orlead of the equipment that is desired to be protected, and abnormalvoltages then travel through said contact member 5 to the serrateddischarge member 2 and bimetal member 3 by way of the projections G and1 on contact member 5. These voltages, if sufiiciently great to. createa hazardous condition, will are from the tips of the serrated dischargemember 2 to the ground element I which is as its name implies, connectedto ground.

ground, and in the event In this manner the voltages are dissipated tothat these abnormal voltages are sustained, the heat created by thearcing to the ground element causes the bimetal member 3 to flex intocontact with ground element I, thereby providing a direct path of fixedlow resistance for said voltages to travel to ground. This patheifectively shorts out the arcing occurring from the serrated membersand as cooling occurs the bimetal member will return to its normalposition. Electrical equipment is in this manner positively and quicklyprotected for the duration of the abnormal voltage, the pro tectivedevice removing itself from the circuit when the necessity forprotection has ceased, namely, when the voltage has been dissipated. Theconstruction of the preferred embodiment shown will now be described indetail.

The refractory insulating member l is com posed of a ceramic materialwhich has been subjected to heat, and a particular material meetingthese requirements which may be used is known as Steatite. However,other forms of composttions of insulating material may be employed asweli.

Insulating member 4 is somewhat elongated. and rectangular in shape. Theupper portion evenly recessed at 8 and the bottom of the recess isdesignated at 9 and upper edges H! are some what fiat and parallel. Inthe under portion, a groove ll runs longitudinally therethrough. In thebottom 9 of recess 8 and extending from bottom 9 to groove H are twoholes 12 and i3. Contact member 5 having projections 6 and "l con nectedto either end thereof is placed in groove it with the projections 6 andI extending upwardly through holes 12 and i3. On the flat bottom 9 ofrecess 8 is placed the somewhat elongated serrated discharge member 2.

The base Id of the serrated member 2 has two apertures therein which arein registry with holes l2 and 13 so that projections 6 and T of contactmember 5 extend upwardly therethru. Along the lateral edges of dischargemember 2, connected to and extending upwardly therefrom are sawtooth-like serrations l5 and IS. The tips of these serrations arepointed and somewhat sharp. At one end of the serrated member andconnected thereto is an upraised hook IT.

The thermal bimetal member 3 is essentially rectangular in shape and ofdimensions somewhat smaller than those of recess 8. The center portion,longitudinally speaking, is cut away with the exception of a cross piecel8 and the end crosspieces thereof. One end has thereon a raised contactis. The other end is then placed under hook I! so that the major portionof the bimetal member normally lies flat on the base ll of the dischargemember 2 and between the upwardly extending serrations I and I6.

Projection 6 extends upward through the cutout center portion of thebimetal element and is bent tightly over cross piece l8. The otherprojection, I, is bent tightly over base ll of discharge member 2 andthe hook i1 is pressed tightly down over the end of the bimetal memberthereunder thereby firmly holding all of these members together.

The bimetal member is so constructed that heat will cause it to flexupwardly, but as one end is securely held or clamped down to therefractory insulating member 4 by bent over projection 6 and hook l1,only the other end having thereon contact l9 can raise upwardly when thebimetal is heated.

The pointed saw teeth-like tips of serrations l5 and iii are upset sothat a predetermined distance exists between a plane including the tipsand the plane including the upper edges Ill of refractory insulatingmember 4.

The device is then completed by placing ground element I, preferably asubstantially rectangular carbon block and of the same dimensions inlength and width as the insulating'member, upon the flat upper edges Hi.In this position, as shown in the cross section in Fig. 3, only a narrowair gap of predetermined size exists between the now upset tips ofserrations i5 and I6 and the under surface of ground element I.

It will also be seen, particularly in this cross sectional view, thenormal position of the bimetal member laying flat upon the base H of thedischarge member 2 and that its free end with contact l9 thereon isnormally out of electrical contact with the under surface of groundelement i.

Looking again at the cross section in Fig. 3, it is now readily seenthat an abnormal potential on contact member 5 will be transmittedthrough projections 6 and l to the serrated discharge member 2 as wellas the bimetal member 3, and that if this potential is above apredetermined value it will complete a path to ground on ground element1 from the nearest points thereto, namely, by arcing from the tips ofserrations l5 and I6. Any sustained abnormal voltage will seek toperpetuate this path and the arcing will create suflicient heating veryquickly to cause bimetal member 3 to flex upwardly so that contact l9will be in electrical contact with ground element I. A fixed lowresistance circuit is thereby traced from the potential on contactmember 5 through the projection Ii to the crossarm 18 of bimetal member3 and therethrough to contact IS on the end thereof to ground element Iand ground thereon. This latter low resistance path effectively shortcircuits the arcing paths previously described and as cooling occurs,the bimetal member 3 will flex back to normal removing the short.

It will be seen therefore that the device will be good for a great manycontinued repetitions of this protective cycle.

Having described my invention in detail what I desire to be protected bythe issuance of Letters Patent of the United States is:

1. A device for protecting electrical equipment from abnormal voltagescomprising in combination, a metallic contact member; a metallicserrated discharge member having a base and a pair of oppositelypositioned serrations extending upwardly from the lateral edges of saidbase; and a bimetal short circuiting member normally lying flat on saidbase and extending longitudinally between said serrations, said bimetalmember be ing additionally arranged with relation to said base in amanner such that heat will cause it to flex upwardly therefrom, all ofsaid members connected mechanically and electrically together, a carbonblock ground element positioned substantially parallel to the base ofsaid serrated member and separated from the tips of the teeth of saidserrations by a small airgap, and ceramic insulator means formaintaining the ground element in said position, whereby an abnormalvoltage on said contact member will travel thru said serrated member anddischarge thru the serrations thereof to said ground element in aplurality of arcs, and in case said arcing is sustained, the heatgenerated therefrom will cause said bimetal member to flex upwardly andcontact said ground element directly shorting said abnormal voltage tosaid ground element.

2. A device for protecting electrical equipment from abnormal voltagesas claimed in claim 1 wherein one end only of said bimetal member issecured to the base of said serrated member, the other end extendingfree therebetween and beyond the longitudinal extent of said serrations,said otherend having a wide contact portion on the extremity thereof,said free end rising and said contact portion engaging said groundelement when the arcing from the serrations to the ground element aresustained.

3. A device for protecting electrical equipment from abnormal voltagesas claimed in claim 1 wherein said bimetal member resumes its positionflat on the base of said serrated member when cooling of said bimetalfollowing said short circuiting has occurred.

4. A device for protecting electrical equipment from abnormal voltagesas claimed in claim 2, said serrations aligned longitudinally, the tipsof said serrations lying in parallel lines which are parallel also tosaid ground element as well as spaced by a narrow air gap therefrom.

5. A device for protecting electrical equipment from abnormal voltages,in combination, a metallic discharge member having a base, oppositelydisposed serrations extending upwardly from the lateral edges of saidbase; a bimetal shorting member normally lying flat on said base andbetween said serrations, a ground element and means for positioning saidground element in spaced relation to said members; a contact memberconnected to said other members and maintaining said discharge memberfixed to said positioning means and clamping one end of said bimetalmember to said base; the other end of said bimetal member free to moveupwardly when heated; and the tips of said serrations being upset toprovide a small air gap between said tips and said ground element,whereby an abnormal potential on said contac member will are from theupset tips of said serrations to said ground element, the heat from saidarcing causing the free end of said bimetal member to move upwardly tocontact the ground element offering a low resistance path therethru toground, effectively shorting said potential thereby to ground.

6. A device for protecting electrical equipment from abnormal voltagescomprising, a ceramic insulating block having a rectangular flatbottomed recess in one surface and a groove in an opposite surface, twoholes joining said recess with said groove, a contact member in saidgroove, two projections connected to either end of said contact memberand extending upwardly therefrom thru said holes into said recess, ametallic discharge member having a base and two apertures therein, saiddischarge member positioned in said recess with its apertures inregistry with said holes and said projections extending therethru, apair of serrations extending upwardly from the lateral edges of saidbase and a raised hook at one end of said base, a bimetal shortingmember having an elongated slot ex tending longitudinally thru thecenter portion thereof and normally lying flat on said base be tweensaid serrations; a cross piece near one end of said slot and that end ofsaid bimetal element held down beneath said hook; the other end of saidbimetal member free to rise upwardly when heated, one of saidprojections bent over said crosspiece co-operating with said hook toclamp said one end of the bimetal member and the discharge member Withinsaid recess to said insulating block, the other projection bent oversaid base additionally securing said discharge mernher to saidinsulating block, a carbon ground element positioned on the edge of saidrecess in spaced relation to said members, and the tips of saidserrations being upset so that they are in a plane parallel to saidgrounding element and separated therefrom by a narrow predeterminedairgap, whereby an abnormal potential on said contact member will arc toground from said upset serration tips, the heat from said arcing causingthe free end of said bimetal member to move upwardly contacting thegrounding element to close a low resistance path ther'ethru from saidabnormal potential to ground.

7. In a device for protecting electrical equipment from abnormalvoltages as claimed in claim 6, a raised wide contact integrallyconnected to said free end of said bimetal member for contacting saidground element when said bimetal member is heated.

8. A device for protecting electrical equipment from abnormal voltages,comprising a refractory insulating block having a recess and a groove inopposite surfaces, said groove connected to said recess by two holesthrough said block; a carbon block for covering said recess; a dischargemember lying in said recess having a base, a pair or" oppositelypositioned serrations extending upwardly from the edges of said base, ahook at one end of said base and a pair of holes in said base; abimetallic short circuiting member normally lying flat in said recessand resting on said dis charge member, said bimetallic member being helddown at one end by said hook and being so constructed as to flexupwardly at the other end so as to contact said carbon block in theevent of an abnormal increase in temperature; and a contact member insaid groove having a pair of projections extending upwardly at eitherend of said member through the holes in said insulating block, saiddischarge member, and said bimetallic member, and bent over at the ends,thereby securely connecting said members mechanically and electricallytogether in spaced relation one to another and in relation to saidcarbon block when said carbon block is set on said insulating member.

THEODORE C. RIEBE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,656,076 Sands Jan. 10, 19282,141,490 Sands Dec. 27, 1938 2,463,718 Sands Mar. 8, 1949

